1. Field of the Invention
The present invention relates to a method and apparatus for estimating a life-span of a cutter by which a sheet member that is conveyed on conveyor rollers or the like, is cut. The sheet member may be a paper strip, thin film, cloth or the like that is adapted for image-formation.
2. Description of the Related Art
In an ordinary thermal-transfer type image-forming apparatus in which an image exposed on a photosensitive material is thermally transferred onto an image-receiving sheet, the photosensitive material is firstly unwound and pulled out by a certain length from a magazine, and thereafter a piece or sheet of photosensitive material is cut off therefrom. The sheet-form piece of photosensitive material is then conveyed to an exposure section.
In the exposure section, an image is exposed onto the photosensitive material. The image-exposed photosensitive material then has water applied thereto, and is thereafter conveyed to a transfer section. In the transfer section, the photosensitive material is overlapped with the image-receiving sheet, wound together with the image-receiving sheet around a heating drum, and pressed onto the heating drum for a predetermined length of time, so that the image on the photosensitive material is thermally transferred to the image-receiving sheet.
The image-receiving sheet is accommodated in a magazine in a wound state. After a predetermined length of the image-receiving sheet has been unwound, a desired length of the image-receiving sheet is cut off by a sheet cutter 92 for cutting the image-receiving sheet, as shown in FIG. 9. The cut-off image-receiving sheet is then conveyed to a transfer section.
The sheet cutter 92 features a rotary blade 98 and a fixed blade 94 with an elongated plate shape. When the rotary blade 98 moves along the fixed blade 94 while rotating, an image-receiving sheet P which is conveyed and disposed over the fixed blade 94 is cut by an engaging portion between the rotary blade 98 and the fixed blade 94.
As the number of cuttings increases, the edge of the rotary blade 98 becomes worn or unfit for use. Due to this wear, during cutting, burrs K and warp would inevitably be generated at an edge of the piece of the image-receiving sheet P, as shown in FIG. 10. Thus, when the sheet piece was overlapped with a photosensitive material, a small space is generated therebetween due to burrs and warp, which might cause a poor picture, e.g., a so-called “white clarity”. Sheet jamming would also be generated due to poor cutting.
At present, in general, the rotary cutter is not regarded as unfit for use and is not replaced until immediately before problems such as poor picture, jamming and the like become apparent. In brief, the method of replacing a cutter in use with a new one is not a systematic method based on predetermined criteria.